We have previously identified by two-dimensional electrophoresis or (35S)-methionine labelled plasma membranes the steady-state and the newly synthesized proteins of that membrane in Dictyostelium discoideum, at a series of developmental stages. We have used cell surface-specific radioiodination to detect externally-exposed proteins. Future studies include: a. Additional characterization of plasma membrane proteins by: 1. isolation of phagosomes to allow identification of proteins on the cytoplasmic face of the plasma membrane; 2. metabolic labelling with radioactive sugar precursors and two-dimensional gels of plasma membranes to identify glycoproteins and the diversity of oligosaccharide distribution among them; 3. pulse and long-term labelling to identify membrane phosphoproteins; 4. identification of methylated membrane proteins by comparison of incorporation of (35S) versus (3H)-methyl methionine. b. Identification of oligomeric membrane proteins by chemical and photochemical crosslinking. c. Initiation of studies with developmental mutants to determine the biochemical/biological role of identified membrane proteins.